Transfer of toxin - coding megaplasmid of bacillus thuringiensis subsp. thompsoni into bacillus sphaericus.

ABSTRACT

Mosquito borne diseases form a major component of vector borne diseases from all over the world. Several control strategies have been adopted to control diseases transmitted by mosquitoes. Bacterial insecticides have been used for the control of nuisance and vector mosquitoes for more than two decades. Nevertheless, due primarily to their high cost and often only moderate efficacy, these insecticides remain of limited use in tropical countries where mosquito-borne diseases are prevalent. Recently, however, recombinant DNA techniques have been used to improve bacterial insecticide efficacy by markedly increasing the synthesis of mosquitocidal proteins and by enabling new endotoxin combinations from different bacteria to be produced within single strains. Both Bacillus sphaericus and Bacillus thuringiensis subsp.thompsoni produce insecticidal toxins during sporulation and are extensively used in the field for control of mosquito populations. All the known toxins of the latter organism are known to be encoded on its megaplasmids. In an attempt to combine the best properties of the two bacteria, a cry proteins (namely 34- and 40-kDa) encoding megaplasmid (~ 100 MDa) of Bt subsp.thompsoni was transferred to Bacillus sphaericus by conjugation. Many of the transconjugants reacted with antibody to the 34- and 40-kDa Bt subsp.thompsoni crystal toxins in western blotting and were more toxic to Aedes mosquitoes than the wild type B. sphaericus. The toxicity of the transconjugants was maintained through many transfers in the absence of selective pressure.